Basemap readshapefile ValueError

Question

I downloaded a map from US Census in shapefile format. It has all the required information that I need, but for som reason there's a specific map that I need it's giving me this error:

Traceback (most recent call last):
  File "C:/Users/Leb/Desktop/Python/Kaggle/mapp.py", line 17, in <module>
    shp_info = m.readshapefile('gis/cb_2014_us_state_5m', 'states', drawbounds=True)
  File "C:\Program Files\Python 3.5\lib\site-packages\mpl_toolkits\basemap\__init__.py", line 2162, in readshapefile
    raise ValueError('readshapefile can only handle 2D shape types')
ValueError: readshapefile can only handle 2D shape types

More specifically these set of files give me the error. As you can see, I downloaded the 5m resolution shapefile.

This is the code that I'm using to execute the command:

import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap as Basemap

m = Basemap(llcrnrlon=-119, llcrnrlat=22, urcrnrlon=-64, urcrnrlat=49,
            projection='lcc', lat_1=33, lat_2=45, lon_0=-95)
shp_info = m.readshapefile('gis/cb_2014_us_state_5m', 'states', drawbounds=True)

Questions:

1. Do I need to convert this through Fiona? or ArcGIS? in order to change it to the proper format.
2. Is there a better alternative to basemap?

Answer 1

The problem is that these cb_ files are lists of shapely 3D PolygonZ objects, and readshapefile needs them to be 2D Polygon objects, even if the Z dimension is all 0's, as is the case with these cb_* files. You can convert them by stripping the Z dimension.

I started to use geopandas as a wrapper around basemap and other utilities and this is how I converted them:

def convert_3D_2D(geometry):
    '''
    Takes a GeoSeries of Multi/Polygons and returns a list of Multi/Polygons
    '''
    import geopandas as gp
    new_geo = []
    for p in geometry:
        if p.has_z:
            if p.geom_type == 'Polygon':
                lines = [xy[:2] for xy in list(p.exterior.coords)]
                new_p = Polygon(lines)
                new_geo.append(new_p)
            elif p.geom_type == 'MultiPolygon':
                new_multi_p = []
                for ap in p:
                    lines = [xy[:2] for xy in list(ap.exterior.coords)]
                    new_p = Polygon(lines)
                    new_multi_p.append(new_p)
                new_geo.append(MultiPolygon(new_multi_p))
    return new_geo

import geopandas as gp
some_df = gp.from_file('your_cb_file.shp')
some_df.geometry = convert_3D_2D(cbsa.geometry)

Install GeoPandas with pip install geopandas. I think that should be it!